The present invention is directed to bicycles and, more particularly, to a bicycle shift control device that inhibits the generation of a second shift signal after the generation of a first shift signal.
In current practice, shifting devices capable of shifting gears electrically or hydraulically are mounted on bicycles. For example, a motor-actuated shifting device is disclosed in JP (Kokai) 8-113182 as an externally mounted shifting device comprising a derailleur and a plurality of sprockets, each sprocket being provided with a different number of teeth and being mounted on the rear wheel. With such shifting devices, and with externally mounted shifting devices such as derailleurs in particular, a chain is moved by the derailleur to one of a large number of sprockets. Such shifting devices provide automatic shifting based on bicycle speed and/or manual shifting based on the manual manipulation of one or more shift control members. A shift signal is generated and output in accordance with the bicycle speed or the manual shifting action, and the motor-actuated derailleur is operated in accordance with the output shift signal.
To allow the chain to move smoothly, promptly, and reliably to any of the sprockets, the sprockets sometimes are provided with special shifting teeth that facilitate the movement of the chain from one sprocket to another, and the shifting teeth of the adjacent sprockets are aligned in phase with each other. The shift signal is generated when the desired inside or outside link of the chain is in proper alignment with such a shifting tooth. In addition, smaller sprockets with a single shifting tooth are commonly provided with an odd number of teeth such that the inside and outside links of the chain alternately align with the shifting tooth with every revolution. Consequently, the shifting operation completes in the course of a single revolution of the sprocket if the shifting tooth is in proper alignment with the outside or inside link during the initial revolution. When, however, the shifting tooth is not in proper alignment with the desired link during the initial revolution, the shifting operation is not completed until another revolution is made and the appropriate link is brought into alignment with the shifting tooth. In this case, a maximum of two rotations is needed until the shifting operation is completed. Providing each sprocket with two or more shifting teeth allows shifting operations to be completed more rapidly in proportion to the number of such teeth.
With conventional devices, it is sometimes impossible to operate a shifting device in a smooth manner during rapid acceleration or deceleration or when multiple gears are shifted at one time. For example, when the brake is abruptly actuated while the bicycle moves at a high speed (and the chain engages a sprocket with a small number of teeth) during automatic shifting, the shifting device may immediately try to change to the gear that corresponds to the desired speed. Not only does the shifting device frequently try to shift multiple gears at a time, but the shifting device also may miss the desired phase-aligned shifting tooth. Such actions produce shocks and prevent the device from operating smoothly. The same problem occurs when gears are manually shifted multiple gears at a time and during rapid acceleration.